This invention relates to microstrip patch antennas and to arrays of such antennas and, more particularly, to a patch antenna assembly having one or more patch radiators with feed structures for radiation of electromagnetic power at any number of frequencies.
Circuit boards comprising a dielectric substrate with one or more metallic, electrically-conductive sheets in laminar form are used for construction of microwave components and circuits, such as radiators of an antenna filters, phase shifters, and other signal processing elements. Different configurations of the circuit boards are available, three commonly used forms of circuit board being stripline, microstrip, and coplanar waveguide. Of particular interest herein is a laminated antenna structure employing microstrip. The microstrip structure is relatively simple in that there are only two sheets of electrically conductive material, the two sheets being spaced apart by a single dielectric substrate. One of the sheets is etched to provide strip conductors which, in cooperation with the other sheet which serves as a ground plane, supports a transverse electromagnetic (TEM) wave.
A laminated structure of microstrip components facilitates manufacture of antenna assemblies and arrays of antenna assemblies on a common substrate. The relatively simple structure of microstrip permits interconnection with a variety of physical shapes of electronic components, particularly for the excitation of radiators in an array antenna. This provides great flexibility in the layout of the components on a circuit board.
Laminated structures of dielectric material with sheets of metal interposed between the dielectric layers or embedded therein are advantageous because of the ease of manufacture which may employ photolithographic techniques. Specific shapes of metallic elements can be attained by photolithography. This form of construction can be used to advantage in the manufacture of microstrip radiator assemblies for use as single antennas or as antenna elements in an array antenna. The antennas may be employed for radar or for communications. A linearly polarized antenna is preferred where higher output power is required, but circularly polarized radiation is preferred, particularly in mobile communication situations to accommodate changing orientations between a transmitter and a receiver of a communication signal. In addition, it is desirable to have dual or multiple frequency capability wherein frequency bands may be separated, or made contiguous for wide band applications.
A problem arises in that an antenna assembly incorporating the foregoing construction features has not been available for dual or multiple frequency operation in cases of linearly and circularly polarized radiation. The construction of such an antenna assembly or array of radiators would be beneficial from a manufacturing point of view and because of utility in radar and communications.